The huge lake upon whose northeastern shore Polonnaruwa rests is an inland sea known as the Parakrama Samudra. The largest irrigation tank of Parakramabahu I. It was the life-blood of the ancient city in the same way that it is the blood life of the religion today, providing water for the growth of thirsty rice crops and other foodstuffs. Its 5,600 acres of  water irrigated an estimated 18,200 acres of paddy land. 

Five minor lakes were incorporated in the building of the Parakrama Samudra, whose 8 1/2- mile bund contains 4 1/2 million cubic yards of earth. One thousand men employed in the hand labor of the period, working 24 hours a day. could scarcely have completed the job in 12 years.